Fluorochemical compounds and their derivatives (sometimes called organofluorine compounds or fluorochemicals) are a class of substances which contain portions that are fluoroaliphatic or fluorocarbon in nature, e.g., nonpolar, hydrophobic, oleophobic, and chemically inert, and which may further contain portions which are functional in nature, e.g., polar and chemically reactive. The class includes some commercial substances which are familiar to the general public, such as those which give oil and water repellency and stain and soil resistance to textiles, e.g., Scotchgard.TM. carpet protector.
An industrial method of producing many fluorinated compounds, such as perfluorinated and partially-fluorinated organofluorine compounds, is the electrochemical fluorination process, commercialized initially in the 1950s by 3M Company, which comprises passing an electric current through a mixture of the organic starting compound and liquid anhydrous hydrogen fluoride. This fluorination process is commonly referred to as the "Simons electrochemical fluorination process," or more simply either the Simons process or electrochemical fluorination (ECF). The Simons ECF process is disclosed in U.S. Pat. No. 2,519,983 (Simons) and is also described in some detail by J. Burdon and J. C. Tatlow in Advances in Fluorine Chemistry (M. Stacey, J. C. Tatlow, and A. G. Sharpe, editors), Volume 1, pages 129-37, Butterworths Scientific Publications, London (1960), by W. V. Childs, L. Christensen, F. W. Klink, and C. F. Kolpin in Organic Electrochemistry (H. Lund and M. M. Baizer, editors), Third Edition, pages 1103-12, Marcel Dekker, Inc., New York (1991), and by A. J. Rudge in Industrial Electrochemical Processes (A. T. Kuhn, editor), pages 71-75, Marcel Dekker, Inc., New York (1967).
Simons ECF can be utilized to prepare fluorinated compounds such as fluorinated carboxylic acid fluorides and fluorinated alkanes. However, a drawback of the process is that side reactions often occur. Such side reactions involve cleavage of carbon-carbon bonds and polymer formation. (See Encylopedia of Chemical Technology, Kirk-Othmer, Third Edition, Volume 10, pages 835-36, John Wiley & Sons (1980).) For example, when fluorinated carboxylic acid fluorides are prepared by ECF, low purity and low yields are often obtained due to the formation of rearrangement and cleavage products. Both T. Abe et al. (in Preparation, Properties, and Industrial Applications of Organofluorine Compounds, edited by R. E. Banks, John Wiley & Sons, page 25, New York (1982)) and I. Rozhkov (in Organic Electrochemistry, edited by H. Lund and M. M. Baizer, Second Edition, Marcel Dekker, Inc., page 815, New York (1983)) report low retention in ECF of branched structures. Tertiary structures in particular may be difficult to maintain, as it is known that such structures undergo rearrangement in strongly acidic environments such as hydrogen fluoride (see, e.g., the discussion by G. A. Olah in Friedel-Crafts and Related Reactions, Volume II, Part 1, Interscience Publishers, pages 41-45, New York (1964) and by J. March in Advanced Organic Chemistry, Third Edition, John Wiley & Sons, pages 141-151, New York (1985)).
Although direct fluorination processes (which employ fluorine gas as the fluorinating agent) can be utilized to minimize cleavage problems and enable the preparation of tertiary carbon-containing fluorochemicals, such processes are more costly than Simons ECF (due to the expense of fluorine manufacture and due to poor fluorine efficiency), more hazardous than Simons ECF (due to the risks associated with the use of the highly reactive fluorine gas), and may yield incompletely-fluorinated product (see, e.g., the Dmowski reference infra). It is therefore highly desirable that modifications of the Simons ECF process be developed which reduce or eliminate the cleavage problems associated with it and which thereby enable the preparation of even tertiary carbon-containing perfluorochemicals by Simons ECF.
U.S. Pat. No. 3,950,235 (Benninger) discloses a method for preparing branched perfluoroalkanes by the electrochemical fluorination of branched perfluoroolefins.
H. Huang et al. (J. Chem. Soc. Perkin Trans. 1 1991, 871) describe the preparation of branched perfluorinated ethers and branched perfluoroalkanoyl fluorides by the direct fluorination of alkanols.
D. C. England et al. (J. Fluorine Chem. 17, 265 (1981)) disclose the preparation of heptafluoro-2,2-bis(trifluoromethyl)pentanoyl fluoride by the reaction of carbonyl fluoride with hexafluoropropene dimer in the presence of silver oxide.
W. Dmowski (J. Fluorine Chem. 49, 281 (1990)) describes the direct fluorination of branched fluorohydrocarbons to provide incompletely-fluorinated products.